1. Field
Embodiments of the present disclosure relate to a turbidity sensor capable of measuring turbidity of an aqueous solution including a liquid detergent as well as an aqueous solution including a powdered detergent and a control method thereof.
2. Description of the Related Art
Some of electric home appliances using water, such as washing machines and dishwashers, have a turbidity sensor to measure turbidity and change a washing operation according to the sensed turbidity. These electric home appliances change number of a washing operation according to the turbidity sensed by the turbidity sensor, thereby reducing waste of water and carrying out an optimal washing operation.
As illustrated in FIGS. 1A and 1B, a turbidity sensor 3 includes one light emitting unit 3a emitting light and one light receiving unit 3b receiving the light emitted from the light emitting unit 3a to measure turbidity of water using intensity of light emitted from the light emitting unit 3a and the intensity of the light received by the light receiving unit 3b. 
That is, when the light emitting unit 3a emits light at a predetermined intensity, the light receiving unit receives light that is not scattered by particles floating in water to measure turbidity of water. Here, the measured turbidity (F) may be obtained as an output of a function represented by Equation 1 below.F (turbidity)=a×(amount of light received by light receiving unit/amount of light emitted from light emitting unit)   Equation 1
In Equation 1, a is a proportional constant. As the turbidity of the water increases, the amount of light received by the light receiving unit 3b becomes smaller than that emitted from the light emitting unit 3a. Thus, the obtained output of Equation 1 decreases.
When the turbidity of water is high, as shown in FIG. 1A, a large amount of light emitted from the light emitting unit 3a is scattered by particles contained in the water, and only a small amount of the light is received by the light receiving unit 3b, and thus the obtained output of Equation 1 decreases. On the other hand, when the turbidity of the water is low, as shown in FIG. 1B, a large amount of the light emitted from the light emitting unit 3a passes through the water and is received by the light receiving unit 3b and thus the obtained output value of Equation 1 increases. FIG. 2 shows output of the turbidity sensor 3 with respect to turbidity of water.
As shown in FIG. 2, as turbidity decreases (C), output of the turbidity sensor 3 increases. On the other hand, as turbidity increases (D), output of the turbidity sensor 3 decreases.
When a powdered detergent is used, outputs of such a conventional turbidity sensor 3, which determines turbidity using light having a wavelength in an infrared range, are accurately distinguishable according to the amount of the powdered detergent and pollution level of water since the particle size of the powdered detergent is large enough.
However, when a liquid detergent is used, outputs of the turbidity sensor 3 are not distinguishable according to the amount of the liquid detergent in comparison with pure water due to a small particle size of the liquid detergent.